Conventionally, a solder containing lead, or lead glass frit has been mainly used as means for bonding and sealing in the technique of bonding glasses and the like. However, lead has become impossible to be used due to environmental problems. On the other hand, among various brazing materials, brazing sheets, and the like described in “JIS Handbook (3) Non-ferrous Metals,” there are no materials, in the present situation, having a melting point of not higher than 400° C., having good adhesiveness, and being capable of bonding without causing the shrinkage cracking in glass due to the difference in thermal expansion coefficient between the glass and a brazing material.
On the other hand, there are applications which require sealing by solder, such as double glazing, vacuum containers, gas sealed containers, and the like, and thus the development of lead-free alloy solder suitable for these applications has been desired.
Recently, In (indium) and an In alloy are proposed for metal sealing materials (see JP-A-2002-020143 and JP-A-2002-542138). An solder alloy containing a large amount of In is proposed, in which many types of elements, such as Al (aluminum), Ag (silver), Cu (copper), and Zn (zinc), are added to Sn (tin) being the main component (see JP-A-2000-141078). Bi based solder comprising Bi (bismuth), Zn, Sb (antimony), Al, In, and the like is also proposed, and further, a solder alloy having a further lower melting point is also proposed (see JP-A-2006-159278).
The solder alloys proposed in JP-A-2002-020143, JP-A-2002-542138, JP-A-2000-141078, and JP-A-2006-159278 have excellent bonding strength and airtight sealing properties to oxide materials, such as glass or ceramic, as lead free solder alloys having a low melting point. However, In is necessarily added, which is poor in its resources. Thus, the approaches in JP-A-2002-020143 and JP-A-2002-542138 are limited in use because they are expensive. Although the approaches in JP-A-2000-141078 and JP-A-2006-159278 allegedly provide effect with the addition of a relatively small amount of In, the alloys contain zinc having high vapor pressure, so that the vacuum container may be contaminated. JP-A-2006-159278 further employs highly noxious antimony (Sb), so that the effect on the human body should be considered in use.
The invention solves the drawbacks as described above, and aims to provide a solder alloy for bonding an oxide having excellent bonding strength, airtight sealing properties and a low melting point, which has a componential system as simple as possible. An oxide joint is also provided using the solder alloy.